Control system



CONTROL SYS TEM Original Filed Aug. 25, 1944 INVENTOR Fkderz'ck 0 Snyder:

ATTORNEY WITNESSES:

Reissued Dec. 17, 1946 22,821 CONTROL SYSTEM Frederick D. Snyder, Milton, Mass, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original N0. 2,397,214, 6

ated March 26, 1946,

Serial No. 551,117, August 25, 1944. Application for reissue September 10, 1946, Serial No.

Claims.

My invention relates to controls for directcurrent shunt motors and aims chiefly at providing a simple and reliable control system that secures a satisfactory dynamic braking of the motor even in cases of voltage failure Or upon accidental or inadvertent interruption of the current supply.

According to the invention, the control and energizing circuit of a reversible direct-current shunt motor is provided with a rectifier and contains a voltage responsive relay which connects the shunt field winding of the motor to the en ergizing current line only when the line voltage is above a safe value but connects the field winding through the rectifier across the motor armature when the line voltage drops below the safe value. As a result, the field winding is excited by armature voltage in the direction to stop the motor whenever the voltage becomes unduly low and regardless of the running direction of the motor at the time of voltage failure.

According to another feature of the invention, a dynamic braking resistor is provided and is controlled by the above-mentioned voltage responsive relay so that it is automatically connected across the armature whenever the relay reacts to voltage failure.

These and other features of the invention will be apparent from the following description of the embodiment illustrated in the drawing.

The drawing shows the circuit diagram of a direct-current shunt motor DM to be used for driving a machine tool or other apparatus which requires a reversal in running direction. The motor DM has an armature I, a main field winding 2 designed as a separately excited shunt field winding and an interpole or compensating series field winding 3.

The motor is energized from the leads LI and L2 of a direct-current line 4 through a main switch 5. The shunt field winding 2 is connected with leads LI and L2 by a relay controlled circuit which includes a discharge resistor 6 and a calibrating rheostat I. Connected with the shunt field winding 2 is further a rectifier unit 8 consisting, for instance, of a bridge arrangement of dry or junction type rectifiers. A resistor 9 is provided for connection across the armature in order to obtain dynamic braking. Two further resistors, denoted by 32 and 42, serve for starting the motor.

The connection of the armature and field windings of the motor with the above-mentioned auxiliary devices is controlled by a system of relays which includes two reversing contactors RC and FC, two accelerating contactors IA and 2A, a brake relay BR and a voltage responsive relay VR. These relays are under control by a reversing master switch denoted by RS.

The line contactors RC and FC have each an to lead L2.

energizing coil Hi and 20, respectively, for actuating two main contacts I, I2 and 2|, 22 and one interlock contact I3 and 23, respectively. The accelerating relays IA and 2A have each a coil 30 and 42 for actuating a contact 3! and 4|, respectively. The brake relay BR has a coil 50 and a control contact 5|. The voltage relay is provided with six contacts denoted by numeral 6| through 56. The master controller has stationary contact fingers, such as those denoted by H, and is provided with contact segments l2, 13, M and '55. These segments are electrically interconnected.

All parts of the illustrated control system are shown in their inoperative positions. For operation, the main switch 5 is closed. This causes a current to flow from lead LI through segment 12 of switch RS, thence through coil of relay VR.

If the line voltage is above the minimum operating value of relay VR, coil 6i] is sufficiently energized to actuate its contacts. As a result, contacts GI and 62 connect field winding 2 across the line through calibrating rheostat 1. At the same time, contacts E3, 64 and 65 are opened so that the rectifier B is disconnected from the armature I. Contact '66 of relay VR closes also and establishes a self-holding circuit for coil 60 of relay VR. The armature I remains deenergized since both contactors RC and FC remain inoperative.

When now the master controller RS is moved from the off position to point I forward, the voltage responsive relay VR remains energized through its contact ure or interruption of current supply occurs. Coil 20 of contactor PC is now energized through segment 13 so that contacts 2|, 22 and 23 are closed. The closure of contacts 2| and 22 connects the armature across the line for operation in the forward running direction. Simultaneously, contact 23 closes the energizing circuit of coil 50 so that contact 5| of the brake relay BR op'ens thereby interrupting thecircuit of resistor 9. Segment M of switch RS provides also energization for coil 39 of accelerating relay IA so that contact 3| short-circuits the starting resistor 32. Hence, only resistor 42 remains effective in the armature circuit. When now turning the switch RS to point 2 forward, coil 40 is also energized through segment 14 so that contact 4| shorts the resistor l2, thereby placing the armature under full excitation.

In order to operate the motor in the reverse direction, switch RS is successively placed on point I and point 2 reverse. This causes the contactor RC to be energized through segment 15 while contactor FC remains inoperative. The accelerating relays IA and 2A become effective in thesame sequence :asdescribed in the foregoing so 66 as long as no voltage failv that the motor accelerates to full speed except that its running direction is reversed.

For stopping the motor switch RS is turned to its oil position. This has the effect of deenergizing the line contactor F or RC so that no further excitation is supplied to armature I. At the same time, the opening of the interlock contact 23 or I3 disconnects coil 50 of brake relay BR so that resistor 9 is connected across armature I and provides for dynamic braking. Under normal 1 conditions, however, the voltage relay VR remains energized through its contact 66 so that the field winding 2 remains connected to the line. 7 If during any of the above-mentioned operating stages the current supply is interrupted or if the energizing voltage drops below the safe value,

the voltage relay VR drops out. This causes contacts GI and 62 to disconn from the line.

closes the rectifier out winding 2.

set the field winding 2 At the same time, theclosure of excited-by the current induced in motor I. Due to the effect of rectifier 8, the current fiow through field winding 2 is always in the direction necessary for stopping the motor regardless of the running direction of the armature. If at the moment of voltage failure, the switch RS is not in its oil position, the dropping out of the voltage relay has also the effect of deenergizing the brake relay BR as well as the reversing contactor FC or RC then in operation. This is due to the fact that in all positions of swit ofi position, the ener extends from line LI when this contact op ch RS, excepting its gization for all relay coils through contact 66. Hence, ens, its interrupts the energizing circuits of relays BR, FC, RC, IA and 2A.

Thus, the armature I is from the line and its illustrated starting 0 closed for dynamic bra the system for opera RS must first be ret order to pick up the current supply is elimi- Consequently, ated for temmay have relatively small It will be understood by those skilled in the art that a system of the t going may be modified as parting from the gist an my invention as set fort ing hereinafter.

I claim as my invention: 1. In combination, a reversible direct-current motor having an armature winding, directlable circuit me armature fr both directi ype described in the foreto details without ded essential features of h in the claims followand a shunt field current supply means, controlans for selectively energizing said om said supply means for operation in ons respectively, energizing means for immediately disconnected circuit is placed into the ondition with relay BR king. In order to readjust tion, the master controller urned to its off position in voltage relay VR which then closes the contact 66, provided the voltage failure or other defect of the nated.

In the above-described manner, the system according to the invention secu the motor whenever the unsafe for obtainin ing, thereby preven or machine driven ing complicated au that the rectifier operation only in and operates each ing period of limited duration. this rectifier arrangement can be r porary loads and hence dimensions.

age is below said magnitude.

2. In combination, a reversible direct-current motor having an armature and a shunt field 0 winding, direct-current supply means, controllable circuit means for selectively energizing said armature from said supply means for operation in both directions respectively, energizing means for said winding, a rectifier circuit, a voltage responsive relay disposed for connecting said winding to said energizing means when the voltage of said supply means is above a given magnitude while connecting said winding a cross said armature through said rectifier circuit when said voltage is below said magnitude, a dynamic braking resistor, and a relay controlled by said voltage responsive relay for connecting said resistor across said armature when said winding is connected across said armature.

3. A motor control system, comprising direct current supply means, a reversible direct-current motor having an armature and a shunt field winding, two line contactors for energizing said armature for operation in both directions respectively, a motor control switch for selectively actuating said contactors respectively, energizing circuit means connected with said supply means for exciting said winding, a rectifier circuit, and a voltage responsive relay disposed for connecting said winding to said energizing means when the voltage of said supply means is above a given magnitude while connecting said winding across said armature through said rectifier circuit when said voltage is below said magnitude, said voltage responsive relay being associated with said switch and said contactors so as to permit actuating the latter only when said winding,

direct-current supply means, controllable circuit means for selectively energizing said armature from said supply means for operation in both directions respectively, energizing means for said winding, a rectifier circuit, a voltage responsive relay disposed for connecting said winding to said energizing means when the voltage of said supply means is above a given magnitude while connecting said Winding across said armature through said rectifier circuit when said voltage is below said magnitude, a dynamic braking resistor, and a relay controlled by said voltage responsive relay for connecting said resistor across said armature only when said voltage is below said magnitude.

5. In combination, a reversible direct-current motor having an armature and a shunt field winding,

direct-current supply means, reversible contact means for connecting said armature to said supply means for operation in both running directions respectively,

said winding being consaid armature.

FREDERICK D. SNYDER. 

